This invention relates to control valves and more particularly to such valves which may be used, for example, to control the operation of a vehicle engine to provide speed control over the vehicle.
In order to provide automatic speed control of a vehicle it is necessary to use a speed monitoring system. The information from this system can be used to vary the fuel supply to the engine in accordance with the demands made on the engine during use and thus control its speed.
The speed monitoring can most conveniently be obtained through the use of electronic circuitry and electrical signals generated in direct proportion to vehicle speed which can be obtained in a number of ways. For example, a magnetic field can be provided to rotate with a vehicle component such as a propeller shaft which moves at a speed directly proportional to the road speed of the vehicle under normal operating conditions. Variations in this magnetic field due to rotation of the propeller shaft will induce electrical signals in a suitable detector such as a coil and these signals can be amplified and used to control the operation of a valve in the vehicle fuel supply as is described more fully below.
For the automatic control of the vehicle to operate effectively it is necessary that both the speed monitoring and valve control be efficient over the whole speed range that can be controlled.
The fuel demand by the engine can be gauged by the degree of vacuum attained in the vehicle inlet manifold and this vacuum utilized to control a servo-mechanism operating on the vehicle throttle.
Automatic control systems known to the Applicant prior to this invention and having solenoid operated valves in the vehicle vacuum line which are of an on-off or proportional type, are affected by variations in engine manifold pressure. Thus an electronic feedback signal is required because there must be a change of vehicle speed before automatic compensation takes place. This leads to slight but annoying speed instability.